A survey on communication networks for electric system automation

146 Pages·2006·5.075 MB·English

by  Gungor V.C., Lambert F.C.

ComputerNetworks50(2006)877–897
www.elsevier.com/locate/comnet
A survey on communication networks for electric
system automation
V.C. Gungor a,*, F.C. Lambert b
aBroadbandandWirelessNetworkingLaboratory,SchoolofElectricalandComputerEngineering,
GeorgiaInstituteofTechnology,Atlanta,GA30332,UnitedStates
bNationalElectricEnergyTesting,ResearchandApplicationsCenter,GeorgiaInstituteofTechnology,
Atlanta,GA30332,UnitedStates
Received18January2006;accepted26January2006
Availableonline21February2006
ResponsibleEditor:I.F.Akyildiz
Abstract
Intoday’scompetitiveelectricutilitymarketplace,reliableandreal-timeinformationbecomethekeyfactorforreliable
deliveryofpowertotheend-users,profitabilityoftheelectricutilityandcustomersatisfaction.Theoperationalandcom-
mercialdemandsofelectricutilitiesrequireahigh-performancedatacommunicationnetworkthatsupportsbothexisting
functionalities and future operational requirements. Inthis respect, sincesuch a communication networkconstitutes the
coreoftheelectricsystemautomationapplications,thedesignofacost-effectiveandreliablenetworkarchitectureiscru-
cial.Inthispaper,theopportunitiesandchallengesofahybridnetworkarchitecturearediscussedforelectricsystemauto-
mation.Morespecifically,InternetbasedVirtualPrivateNetworks,powerlinecommunications,satellitecommunications
andwirelesscommunications(wirelesssensornetworks,WiMAXandwirelessmeshnetworks)aredescribedindetail.The
motivation of this paperis to provide a betterunderstanding of the hybridnetwork architecture that canprovide heter-
ogeneouselectricsystemautomationapplicationrequirements.Inthisregard,ouraimistopresentastructuredframework
forelectricutilitieswhoplantoutilizenewcommunicationtechnologiesforautomationandhence,tomakethedecision-
makingprocess moreeffectiveand direct.
(cid:2)2006Elsevier B.V.All rightsreserved.
Keywords: Electric system automation; Internet based Virtual Private Network; Power line communication; Satellite communication;
Wirelesssensornetworks;Wirelessmeshnetworks;WiMAX
1. Introduction
Electricutilities,particularlyinurbanareas,con-
tinuously encounter the challenge of providing reli-
* Correspondingauthor.Tel.:[phone];fax:[phone]
able power to end-users at competitive prices.
7883.
Equipmentfailures,lightningstrikes,accidents,and
E-mail addresses: [email protected] (V.C. Gungor),
[email protected](F.C.Lambert). natural catastrophes all cause power disturbances
1389-1286/$-seefrontmatter (cid:2)2006ElsevierB.V.Allrightsreserved.
doi:10.1016/j.comnet.2006.01.005
878 V.C.Gungor,F.C.Lambert/ComputerNetworks50(2006)877–897
and outages and often result in long service inter- is spread over a large number of users while simul-
ruptions. Electric system automation, which is the taneously providing the benefits of a dedicated pri-
creationofareliableandself-healingelectricsystem vate network. Therefore, Internet VPN technology
thatrapidlyrespondstoreal-timeeventswithappro- as a high speed communication core network can
priateactions,aimstomaintainuninterruptedpower be utilized to enable minimum cost and highly
service[6].Theoperationalandcommercialdemands reliable information sharing for automation
of electric utilities require a high-performance data applications.
communicationnetworkthatsupportsbothexisting AlthoughInternetVPNtechnologiescanprovide
functionalitiesandfutureoperationalrequirements. the necessary reliable communication for substa-
Therefore, the design of the network architecture is tions in urban areas, this may not be the case for
crucialtotheperformanceofthesystem. substationsinremoterurallocationswherethehigh
Recent developments in communication technol- speed communication core network, e.g., Internet,
ogies have enabled reliable remote control systems, might not exist. Therefore, when the individual
which have the capability of monitoring the real- communicationcapabilitiesandlocationsofelectric
time operating conditions and performance of elec- systems are taken into account, it is appropriate to
tricsystems.Thesecommunicationtechnologiescan consider the overall communication infrastructure
beclassifiedintofourclasses,i.e.,PowerLineCom- asahybridnetworkasshowninFig.1.Thishybrid
munication, Satellite Communication, Wireless network consists of two separate parts:
Communication, and Optical Fiber Communica-
tion. Each communication technology has its own • Highspeedcommunicationcorenetwork:Itcanbe
advantages and disadvantages that must be evalu- either a private network or public network. Due
ated to determine the best communication technol- to several technical advantages [32], Internet
ogy for electric system automation. In order to basedVirtualPrivateNetworkcanbeconsidered
avoid possible disruptions in electric systems due asacost-effectivehighspeedcommunicationcore
to unexpected failures, a highly reliable, scalable, network for electric system automation.
secure, robust and cost-effective communication • Lastmile connectivity:It represents the challenge
network between substations and a remote control of connecting the substations to the high speed
center is vital [11,14]. This high performance com- communication core network. The communica-
munication network should also guarantee very tion technologies for last mile connectivity can
strict Quality of Service (QoS) requirements to pre- be classified as: (i) Power line communication,
vent the possible power disturbances and outages (ii) Satellite communication, (iii) Optical fiber
[10]. communication, and (iv) Wireless communica-
When the communication requirements of elec- tion. Each possible communication alternatives
tric system automation are considered, Internet for last mile connectivity introduces its own
can offer an alternative communication network to advantages and disadvantages.
remotely control and monitor substations in a
cost-effective manner with its already existing com- Manyresearchersandseveralinternationalorga-
munication infrastructure. However, Internet can- nizationsarecurrentlydevelopingtherequiredcom-
not guarantee very strict QoS requirements that munication technologies and the international
the automation applications demand, since data communication standard for electric system auto-
communication in Internet is based on best effort mation. In Fig. 2, the summary of these communi-
service paradigm [32]. Furthermore, when a public cation system development activities is presented
network like the Internet is utilized to connect the [14]. Despite the considerable amount of ongoing
substationstoaremotecontrolcenter,securitycon- research,therestillremainssignificantlychallenging
cerns arise. In this context, Internet based Virtual tasks for the research community to address both
Private Network (Internet VPN) technologies, benefits and shortcomings of each communication
which are transforming the Internet into a secure technology. Since a cost-effective data communica-
high speed communication network, constitute the tionnetworkconstitutesthecoreoftheautomation
cornerstone for providing strict QoS guarantees of applications, in this paper, the opportunities and
electricsystemautomationapplications[7].Internet challenges of a hybrid network architecture are
VPN technologies offer a shared communication describedforautomationapplications.Morespecif-
networkbackboneinwhichthecost ofthenetwork ically, Internet based Virtual Private Networks,
V.C.Gungor,F.C.Lambert/ComputerNetworks50(2006)877–897 879
Fig.1. Theoverallcommunicationnetworkarchitectureforelectricsystemautomation.
Fig.2. Summaryofcommunicationsystemdevelopmentactivitiesforelectricutilities.
power line communications, satellite communica- networks, WiMAX, and wireless mesh networks)
tions and wireless communications (wireless sensor arediscussedindetail.Themotivationofthispaper
880 V.C.Gungor,F.C.Lambert/ComputerNetworks50(2006)877–897
is to provide a better understanding of the hybrid objective,theInternetVPNsolutionshouldprovide
network architecture that can provide heteroge- the following essential performance attributes:
neous electric system automation application
requirements. In this respect, our aim is to present • Quality of Service (QoS): Internet technology
a structured framework for electric utilities who itself cannot guarantee very strict QoS require-
plan to utilize new communication technologies mentsthatutilityapplicationsrequire,sincedata
for automation and hence, to make the decision- communicationintheInternetismainlybasedon
making process more effective and direct. a best effort service paradigm. In this respect,
The remainder of the paper is organized as fol- QoS capabilities of Internet VPN technologies
lows. In Section 2, the benefits and open research ensure the prioritization of mission critical or
challenges of Internet based Virtual Private Net- delay sensitive traffic and manage network con-
works are discussed for electric system automation. gestion under varying network traffic conditions
In Section 4, both advantages and disadvantages over the shared network infrastructure.
of alternative communication technologies are • Reliability: The communication network should
described for last mile connectivity. In Sections 5 beabletooperatecontinuouslyoveranextended
and 6, the opportunities and challenges of wireless period of time, even in the presence of network
sensor networks, wireless mesh networks and element failures or network congestion. To
WiMAX are explained, respectively. Finally, the achieve this, the communication network should
paper is concluded in Section 7. be properly designed with the objective of no
losses in all working conditions and able to deal
with failure gracefully. Service providers support
2. Internet based Virtual Private Networks Service Level Agreements (SLAs), which define
the specific terms and performance metrics
Recent advances in Internet technology and regarding availability of network resources and
Internet-readyIEDs(IntelligentElectronicDevices) offer the Internet VPN subscriber a contractual
have enabled cost-effective remote control systems, guarantee for network services and network
whichmakesitfeasibletosupportmultipleautoma- uptime. Therefore, Internet VPN technology
tionapplicationservices,e.g.,remoteaccesstoIED/ should deliver data in a reliable and timely
relayconfigurationports, diagnosticeventinforma- manner for automation applications.
tion, video for security or equipment status assess- • Scalability: Since the number of substations and
ment in substation and automatic metering. While remote devices is large and growing rapidly, the
traditional private Supervisory Control and Data communication system must be abletodealwith
Acquisition (SCADA) systems constitute the core verylarge network topologies without increasing
communication network of today’s electric utility the number of operations exponentially for the
systems,theInternetbasedVirtualPrivateNetwork communication network. Thus, the designed
(Internet VPN) technology provides an alternative hybrid network architecture should scale well to
cost-effective high speed communication core accommodate new communication requirements
network for remote monitoring and control of the driven by customer demands.
electric system. • Robustness: In order to avoid deteriorating
Specifically,InternetVPNtechnologyisashared communication performance due to changing
communication network architecture, in which the networktrafficconditions,thedimensioningpro-
cost of the network is spread over a large number cess to assign the bandwidth to the virtual links
of users while simultaneously providing both the of the Internet VPN should be based not only
functionalities and the benefits of a dedicated pri- on the main bandwidth demand matrix, but also
vate network. Therefore, the main objective of an onotherpossiblebandwidthdemandmatricesto
Internet VPN for electric system automation is to provide a safe margin in network dimensioning
providetherequiredcost-effectivehighperformance toavoidcongestion[28].Incasethenetworkcon-
communicationbetweenIEDsandaremotecontrol gestion can not be avoided with the current net-
centeroverasharednetworkinfrastructurewiththe work traffic, low priority non-critical data
samepoliciesandserviceguaranteesthattheelectric trafficshouldbeblockedsothatthemostcritical
utility experiences within its dedicated private data can be transmitted with QoS guarantees
communication network. In order to achieve this [26]. This way, additional bandwidth for high
V.C.Gungor,F.C.Lambert/ComputerNetworks50(2006)877–897 881
priority data becomes available to enable the described above. As shown in Fig. 3, each Internet
real-time communication of critical data, which VPN technology supports the performance
isparticularlyimportantincaseofalarmsinelec- attributes to varying degrees and thus, the most
tric systems. appropriate choice depends on the specific commu-
• Security: Security is the ability of supporting nication requirements of the electric utilities.
secure communication between a remote control In Fig. 4, a decision tree for choosing an appro-
centerandfielddevicesinordertomakethecom- priate Internet VPN technology for electric system
munication safe from external denial of service automation is illustrated. As shown in Fig. 4, if an
(DoS) attacks and intrusion. When a public net- electric utility requires a high performance commu-
work like the Internet is utilized to connect the nicationnetworkensuringverystrictQualityofSer-
field devices to a remote control center, security vice (QoS) requirements, the next decision point in
concerns can arise. Hence, Internet VPN has to the decision tree can be the size of the communica-
provide secure data transmission across an exist- tion network, i.e., the number of communication
ing shared Internet backbone and thus, protect entities that need to be interconnected. Electric
sensitive data so that it becomes confidential utilitiesthatneedtoconnectalargenumberofsub-
across the shared network. stations and a remote control center should prefer
• Network management: In order to provide the cost-effective MPLS based Internet VPN technol-
communication requirements of automation ogy, since they can reduce the communication cost
applications, electric utilities demand flexible significantly compared to dedicated private leased
and scalable network management capabilities. communication lines. If the number of sites is not
The primary network management capabilities large in the network, electric utilities can utilize a
of Internet VPN include: (i) bandwidth provi- hybrid network including IPSec Internet VPN and
sioning, (ii) installing security and QoS policies, layer 2 technologies such as Frame Relay and
(iii) supporting Service Level Agreements, (iv) ATM for the automation applications. If there are
fault identification and resolution, (v) addition no QoS communication requirements, the possible
and removal of network entities, (vi) change of options include either using public Internet when
network functions, (vii) accounting, billing and no secure communication is required or using an
reporting. In addition to these network manage- IPSec Internet VPN when secure communication
ment capabilities, Internet VPN technology can is required in automation applications.
enable rapid implementation and possible modi- Infact,theactualselectionofInternetVPNtech-
fications of the communication network at a nology depends on several factors such as the cost
reasonable cost. Therefore, Internet VPN tech- of communication architecture, geographic cover-
nology with effective network management age of the communication architecture, the loca-
approachesprovidesaflexiblecost-effectivesolu- tions of substations and a remote control center,
tionthatcanbeeasilyadaptedtofuturecommu- service level agreements, network management
nication requirements that utility automation types, i.e., customer based or network based man-
applications demand. agement, etc. As a result, electric utilities should
evaluate their unique communication requirements
Despite the extensive research in Internet VPN and the capabilities of Internet VPN technologies
technologies [32], there are still several open comprehensively in order to determine the best
research issues, e.g., efficient resource and route Internet VPN technology for automation
management mechanisms, inter-domain network applications.
management,thatneedtobedevelopedforautoma-
tion applications. In the current literature, two 3. Last mile connectivity for electric utilities
unique and complementary VPN architectures
based on Multi Protocol Label Switching (MPLS) In this section, both advantages and disadvan-
and IP Security (IPsec) technologies are emerging tages of possible communication technologies for
to form the predominant communication frame- last mile connectivity are explained in detail. The
workfordeliveryofhighperformanceVPNservices communication technologies evaluated for last mile
[32].InFig.3,wecompareboththeadvantagesand connectivity are: (i) Power line communication, (ii)
disadvantagesofMPLSbasedVPNandIPSecVPN Satellite communication, (iii) Optical fiber commu-
architectures in terms of performance attributes nication, (iv) Wireless communication.
882 V.C.Gungor,F.C.Lambert/ComputerNetworks50(2006)877–897
Fig.3. ComparisonofMPLSbasedInternetVPNandIPSecInternetVPNforelectricsystemautomationapplications.
Fig.4. AbasicInternetVPNdecisiontreeforelectricsystemautomation.
V.C.Gungor,F.C.Lambert/ComputerNetworks50(2006)877–897 883
3.1. Power Line Communication bit error rates during communication which
severely degrade the performance of PLC.
Power Line Communication (PLC) is transmis- • Capacity: New technological advances have
sion of data and electricity simultaneously over recently enabled a prototype communication
existing power lines as an alternative to construct- modemwhichachievesamaximumtotalcapacity
ing dedicated communications infrastructure. of 45Mbps in PLC [1]. However, since power
Although PLC has been in operation since the line is a shared medium, the average data rate
1950s as low data rate services such as remote con- perenduserwillbelowerthanthetotalcapacity
trol of power grid devices, it has become more depending on coincident utilization, i.e., the
important in recent years due to developments in numberofusersonthenetworkatthesametime
technology, which enable PLC’s potential use for and the applications they are using. Thus, possi-
high speed communications over medium (15/ ble technical problems should be comprehen-
50kV) and low (110/220V) voltage power lines sively addressed with various field tests before
[5]. However, there are still several technical prob- the PLC technology is widely deployed.
lems and regulatory issues that are unresolved. • Open circuit problem: Communication over the
Moreover, a comprehensive theoretical and practi- power lines is lost with devices on the side of
cal approach for PLC is still missing and there are an open circuit [14]. This fact severely restricts
only a few general results on the ultimate perfor- the usefulness of PLC for applications especially
mance that can be achieved over the power line involving switches, reclosers and sectionalizers.
channel. As a result, commercially deployable, high • Signal attenuation and distortion: In power lines,
speed, long distance PLC still requires further the attenuation and distortion of signals are
researcheffortsdespitethefactthatPLCmightpro- immense due to the reasons such as physical
vide an alternative cost-effective solution to the last topology of the power network and load imped-
mile connectivity problem. In the following, we ance fluctuation over the power lines. In addi-
explain both advantages and disadvantages of tion, there is significant signal attenuation at
power line communication technologies for auto- specific frequency bands due to wave reflection
mation applications. at the terminal points [12]. Therefore, the com-
munication over power lines might be lost due
3.1.1. Advantages to high signal attenuation and distortion.
• Security: There are some security concerns for
• Extensivecoverage:PLCcanprovideanextensive PLC arising from the nature of power lines [22].
coverage, since the power lines are already Powercablesarenottwistedandusenoshielding
installed almost everywhere. This is advanta- which means power lines produce a fair amount
geous especially for substations in rural areas of Electro Magnetic Interference (EMI). Such
where there is usually no communication EMI can be received via radio receivers easily.
infrastructure. Therefore, the proper encryption techniques
• Cost: The communication network can be estab- must be used to prevent the interception of
lished quickly and cost-effectively because it critical data by an unauthorized person.
utilizes the existing wires to carry the communi- • Lack of regulations for broadband PLC: In addi-
cation signals. Thus, PLC can offer substations tion to technical challenges, fundamental regula-
new cost-saving methods for remotely monitor- tion issues of PLC should be addressed for
ing power uses and outages. substantial progress to be made. The limits of
transmitted energy and frequencies employed
3.1.2. Disadvantages for PLC should be determined in order to both
providebroadbandPLCandpreventtheinterfer-
• High noise sources over power lines: The power ence with already established radio signals such
lines are noisy environments for data communi- as mobile communications, broadcasting
cations due to several noise sources such as elec- channels and military communications. In this
trical motors, power supplies, fluorescent lights respect,theInstituteofElectricalandElectronics
and radio signal interferences [27]. These noise Engineers (IEEE) has started to develop a stan-
sources over the power lines can result in high dard to support broadband communications
884 V.C.Gungor,F.C.Lambert/ComputerNetworks50(2006)877–897
overpowerlines[18].Thestandardistargetedfor 3.2.2. Disadvantages
completion in mid 2006.
• Longdelay:Theround-tripdelayinsatellitecom-
3.2. Satellite communication munication, especially for Geostationary Earth
Orbit (GEO) satellites,1 is substantially higher
Satellite communication can offer innovative than that of terrestrial communication links.
solutionsforremotecontrolandmonitoringofsub- The transport protocols developed for terrestrial
stations. It provides an extensive geographic cover- communication links such as TCP are not suit-
age, and thus, can be a good alternative able for satellite communication, since necessary
communication infrastructure for electric system data rate adjustments of TCP can take a long
automation in order to reach remote substations time in high-delay networks such as satellite net-
where other communication infrastructures such as works [16]. On the other hand, it is possible to
telephone or cellular networks might not exist. In reduce the round-trip delay by using satellites in
practical applications, Very Small Aperture Termi- lower orbits. Particularly, LEO satellites offer
nal (VSAT) satellite services are already available significantly reduced delay, which is comparable
that are especially tailored for remote substation to that of terrestrial networks.
monitoring applications [33]. Furthermore, with • Satellite channel characteristics: Different from
the latest developments in electric system automa- cabled and terrestrial network communications,
tion, satellite communication is not only used for satellite channels characteristics vary depending
remote control and monitoring of substations but on the weather conditions and the effect of fad-
also used for Global Positioning System (GPS) ing, which can heavily degrade the performance
based time synchronization, which provides micro- of the whole satellite communication system
second accuracy in time synchronization [38]. In [16]. Therefore, these communication challenges
addition, satellites can be used as a backup for the should be taken into account while evaluating
existing substations communication network. In the communication technologies for electric
case of congestion or link failures in communica- system automation.
tion, critical data traffic can be routed through • Cost:Although satellite communication can be a
satellites [8]. In the following, we present both cost-effective solution for remote substations if
advantagesanddisadvantagesofsatellitecommuni- any other communication infrastructure is not
cation technologies. available, the cost for operating satellites (the
infrastructure cost and monthly usage cost) for
3.2.1. Advantages all substation communication networks is still
higherthanthatofotherpossiblecommunication
• Global coverage: Satellite communication sup- options. High initial investment for satellite
ports a wide geographical coverage (including transceivers is one of the limitations of satellite
remote,rural,urbanandinaccessibleareas)inde- communication.
pendent of the actual land distance between any
pair of communicating entities. In case no com- 3.3. Optical fiber communication
munication infrastructure exists, especially for
remote substations,satellite communication pro- Opticalfibercommunicationsystems,whichwere
vides a cost-effective solution. firstintroducedinthe1960s,offersignificantadvan-
• Rapidinstallation:Satellite communication offers tages over traditional copper-based communication
clear advantages with respect to the installation systems. In electric system automation, an optical
of wired networks. A remote substation can join fibercommunicationsystemisoneofthetechnically
a satellite communication network by only attractivecommunicationinfrastructures,providing
acquiring the necessary technical equipment extremely high data rates. In addition, its Electro
without the need for cabling to get high-speed Magnetic Interference (EMI) and Radio Frequency
service [20]. Cabling is not a cost-effective nor a
simple job when the substation is located in a
1 Satellites can be classified into Geostationary Earth Orbit
remote place. Due to economical reasons, some
(GEO)satellite,MiddleEarthOrbit(MEO)satellite,LowEarth
utilities have already installed satellite communi-
Orbit (LEO) satellite according to the orbit altitude above the
cation for rural substations monitoring [33]. earth’ssurface[9].
V.C.Gungor,F.C.Lambert/ComputerNetworks50(2006)877–897 885
Interference(RFI)immunitycharacteristicsmakeit error rates (BER=10(cid:2)15) in fiber optic commu-
an ideal communication medium for high voltage nication are observed. Due to high bandwidth
operating environment in substations [14]. Further- capacity and low BER characteristics, optical
more, optical fiber communication systems support fiber is used as the physical layer of Gigabit
longdistancedatacommunicationwithlessnumber and 10 Gigabit ethernet networks.
of repeaters2 compared to traditional wired net- • Immunity characteristics: Optical fibers do not
works. This leads to reduced infrastructure costs radiate significant energy and do not pick up
for long distance communication that substation interference from external sources [13]. Thus,
monitoring and control applications demand. For compared to electrical transmission, optical
example, the typical T-1 or coaxial communication fibers are more secure from tapping and also
systemrequiresrepeatersaboutevery2kmwhereas immune to EMI/RFI interference and crosstalk.
opticalfibercommunicationsystemsrequirerepeat-
ers about every 100–1000km [13]. 3.3.2. Disadvantages
Although optical fiber networks have several
technical advantages compared to other wired net- • Cost: Although fiber optic networks possess sev-
works, the cost of the optical fiber itself is still eral technical advantages, the cost of its installa-
expensive to install for electric utilities. However, tion might be expensive in order to remotely
the enormous bandwidth capacity of optical fiber control and monitor substations. However, fiber
makes it possible for substations to share the band- optic networks might be a cost-effective commu-
width capacity with other end users which signifi- nication infrastructure for high speed communi-
cantly helps to recover the cost of the installation. cation network backbones, since optical fibers
Inthisrespect,opticalfibercommunicationsystems are already widely deployed in the communica-
might be cost-effective in the high speed communi- tion network backbones and the cost is spread
cation network backbone since optical fibers are over a large number of users.
alreadywidelydeployedincommunicationnetwork
backbones and the cost is spread over a large num- 3.4. Wireless communication
ber of users. As a result, fiber optic networks can
offer high performance and highly reliable commu- Severalwirelesscommunicationtechnologiescur-
nication when strict QoS substations communica- rently exist for electric system automation [14].
tion requirements are taken into account. In the Whencomparedtoconventionalwiredcommunica-
following, we describe both advantages and disad- tionnetworks,wirelesscommunicationtechnologies
vantages of optical fiber communication for auto- have potential benefits in order to remotely control
mation applications. and monitor substations, e.g., savings in cabling
costs and rapid installation of the communication
3.3.1. Advantages infrastructure. On the other hand, wireless commu-
nication is more susceptible to Electro Magnetic
• Capacity: Extremely high bandwidth capacity of Interference (EMI) and often has limitations in
optical fiber communication can provide high bandwidthcapacityandmaximumdistancesamong
performance communication for automation communication devices. Furthermore, since radio
applications. Current optical fiber transmission waves in wireless communication spread in the air,
systemsprovidetransmissionratesupto10Gbps eavesdropping can occur and it might be a threat
using single wavelength transmission and forcommunicationsecurity.Electricutilitiesexplor-
40Gbps to 1600Gbps using wavelength division ing wireless communication options have two
multiplexing3 (WDM). In addition, very low bit choices; (i) utilizing an existing communication
infrastructureofapublicnetwork,e.g.,publiccellu-
lar networks, (ii) installing a private wireless
2 Inlongdistancecommunications,itisnecessarytointroduce network.
repeatersperiodicallyinordertocompensatefortheattenuation Utilizing an existing communication infrastruc-
anddistortionofthecommunicationsignals. ture of a public network might enable a cost-effec-
3 Wavelength division multiplexing (WDM) is an effective
tive solution due to the savings in required initial
approachtoexploitthebandwidthcapacityavailableinoptical
investment for the communication infrastructure.
fiber. In WDM, multiple wavelengths are used to carry several
datastreamssimultaneouslyoverthesamefiber. Ontheotherhand,privatewirelessnetworksenable
886 V.C.Gungor,F.C.Lambert/ComputerNetworks50(2006)877–897
electricutilitiestohavemorecontrolovertheircom- bandwidth capacity is supported and high bit
municationnetwork. However,privatewirelessnet- error rates (BER=10(cid:2)2–10(cid:2)6) are observed in
works require a significant installation investment communication. In addition, since wireless com-
as well as the maintenance cost [14]. In electric sys- munication is in a shared medium, the applica-
tem automation, wireless communication technol- tion average data rate per end user is lower
ogy has already been deployed. Recently, Short than the total bandwidth capacity, e.g., maxi-
Message Service (SMS) functionality of the digital mumdatarateofIEEE802.11bis11Mbpswhile
cellular network has been applied in orderto remo- the average application data rate is approxi-
tely control and monitor substations [34]. The con- mately 6Mbps [21]. Therefore, each level in the
trolchannelofthecellularnetworkisalsoutilizedin communication protocol stack should adapt to
some alarm-based substation monitoring cases [23]. wireless link characteristics in an appropriate
However, both of these communication technolo- manner, taking into account the adaptive strate-
gies are suited to the applications that send a small gies at the other layers, in order to optimize net-
amount of data and thus, they can not provide the work communication performance.
strict Quality of Service (QoS) requirements that • Security: Wireless communication poses serious
real time substation monitoring applications security challenges since the communication sig-
demand. In the following, we describe both advan- nals can be easily captured by nearby devices.
tages and disadvantages of wireless communication Therefore, efficient authentication and encryp-
technologies. tion techniques should be applied in order to
provide secure communication.
3.4.1. Advantages
Note that with the recent advances in wireless
• Cost: Utilizing an existing wireless communica- communications and digital electronics, hybrid net-
tionnetwork,e.g.,cellularnetwork,mightenable workarchitectureshaveenabledalternativescalable
a cost-effective solution due to the savings in wirelesscommunicationsystems,whichcanprovide
required initial investment for the communica- strictqualityofservice (QoS)requirementsofauto-
tion infrastructure. In wireless communication, mation applications. The details of these recent
cabling cost is also eliminated. wireless technologies, i.e., wireless sensor networks,
• Rapid installation: The installation of wireless WiMAXandwirelessmesh networks,aredescribed
communication is faster than that of wired net- in the following sections.
works. Wireless communication provides more
flexibility compared to wired networks. Within 4. Wireless sensor networks for automation
radio coverage, communication entities can start
to communicate after a short communication In this section, we explain the opportunities and
infrastructure installation. challenges of wireless sensor networks (WSNs) and
presentdesignobjectivesandrequirementsofWSNs
3.4.2. Disadvantages for electric system automation applications. In gen-
eral, wireless sensor networks are composed of a
• Limited coverage: Private wireless networks pro- largenumberoflowcost,lowpowerandmultifunc-
vide a limited coverage, e.g., the coverage of tional sensor nodes that are small in size and com-
IEEE 802.11b is approximately 100m [21]. On municate un-tethered over short distances [4]. The
the other hand, utilizing existing public wireless ever-increasing capabilities of these tiny sensor
network, e.g. cellular network, or WiMAX tech- nodes enable capturing various physical informa-
nology can support much more extensive cover- tion, e.g., noise level, temperature, vibration, radia-
age compared to wireless local area networks. tion, etc., as well as mapping such physical
However, some geographical areas, e.g., remote characteristics of the environment to quantitative
rural locations, may still not have any wireless measurements. The collaborative nature of WSNs
communication services. brings several advantages over traditional sensing
• Capacity: Wireless communication technologies including greater fault tolerance, improved accu-
provide typically lower QoS compared to wired racy, larger coverage area and extraction of local-
communication networks. Due to limitations ized features. In this respect, wireless sensor
and interference in radio transmission, a limited networks enable low cost and low power wireless